I agree wholeheartedly. Since I don't play these games all in one go, whenever I return I had a hard time remember who and what they were all about. This problem is exacerbated by the fact that many of them are shallow, one-dimensional characters with essentially no character background that had minimum story impact. They're forgettable characters that didn't leave an impression.
Don't get me wrong, one-off characters for the quick, fuck-of-the-day moments aren't necessary bad of themselves, but only if used sparingly. This way their moment in the sun would be quite striking or attention-grabbing, and could emphasis those moments where the couple have reached a new turning point or milestone.
However, seeing how the game has progressed as far as it did, I'd instead welcome the inclusion of a new, in-game button to help players to refresh their memories. This button could be called "Characters" or something similar, and details who they are, when they were encountered, and what did s/he do with our protagonists thus far. And if there are repeat encounters or if the relationships between those characters and the couple evolves, then they would be reflected in this section with updated notes to the respective character. Heck, it could even show a simple stat like how many times that particular character "banged" either one of the couple.
Some kind of dossier would be nice, is all, considering the vast cast within this game.